Electromechanical machines such as alternator, motor, dynamo, and generator can convert energy between mechanical energy and electrical energy. For example, an electric motor uses electrical energy to produce mechanical energy, and a generator or dynamo uses mechanical energy to produce electrical energy. In general, an electromechanical machine can operate as a motor or as a generator, depending on the applied input energy. The major differences between a motor and a generator can be in the desired optimization, for example, a motor is designed to optimize speed or torque, and a generator is designed to optimize power generation. Thus the following descriptions are directed to electromechanical machine, which can be equally applied to motors and generator.
The electromechanical machine can convert between mechanical energy and electrical energy through magnetic interaction. From a mechanical point of view, the electromechanical machine comprises a stator which is a stationary part, and a rotor which is a rotating part. For example, a motor converts electrical power to mechanical power in its rotor, through a power supplied to the stator and/or the rotor. From an electrical point of view, the electromechanical machine comprises an armature which is the power-producing component (and which can be either the rotor or the stator), and the field component which is the magnetic field component (and which can also be either the rotor or the stator and can be either an electromagnet or a permanent magnet). The following descriptions use rotor and stator in describing electromechanical machine, which can be equally applied to armature and field component. In addition, the following descriptions sometimes use the term “magnetic component” or “magnetic plane” of an electromechanical machine to represent the stator, the rotor, the armature or the field component.
Electrical machines may take the form of DC motors or AC motors with various types such as induction, brushed, brushless, universal, stepper, linear, unipolar, reluctance. However, this classification is not a rigid distinction, especially with advances in electronic control, e.g., moving the commutator out of the motor shell.
There are several ways to supply/generate power to/from an electromechanical machine. In a motor, the supplied power can be from a DC source (DC motor), an AC source (AC motor), or induced in the rotating device (induction motor). AC source can be single-phase or polyphase power systems. For example, two-phase electrical power can have 4 or 3 wires to provide 2 voltage phases, differing by 90 degrees. Three-phase electric power provides 3 voltage phases, differing by 120 degrees. Polyphase power can provide any number of phases, usually three, or a multiple of three.
In addition, motors can incorporate single or double multiphase winding set that is connected to a power supply. For example, doubly-fed electric motors have two independent multiphase windings that actively participate in the energy conversion process, and thus can provide twice the constant torque speed range as singly-fed electric machines.